The invention generally relates to a method for sealing a battery container.
Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized; the cathode contains or consumes an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When a battery is used as an electrical energy source in a device, such as a cellular telephone, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
In a metal-air electrochemical cell, oxygen is reduced at the cathode, and a metal is oxidized at the anode. Oxygen is supplied to the cathode from the atmospheric air external to the cell through one or more air access port(s) in the cell container.
A cylindrical metal-air battery can be assembled by inserting a cathode, a separator, and an anode into a battery container. The end of the container is then sealed. During the sealing process, force must be applied to the container to seal the end. If this force is transferred to the cathode, the cathode can be deformed. When this occurs, electrolyte can sometimes leak from the cell.
The invention features methods for sealing battery containers that minimize damage to the cathode. The invention also features batteries made using these methods.
In one aspect, the invention features a method of sealing an end of a battery container. The method includes: (a) providing a plurality of supports in a wall of the container toward the end of the container; (b) scoring the wall of the container at a position between the end of the container and the supports; (c) inserting a top assembly into the container such that the top assembly contacts the supports; and (d) folding an edge of the container over the top assembly. The supports can be formed, e.g., by half-shearing, lancing, or swaging portions of the container wall.
The supports provide flat surfaces, or xe2x80x9cshelves,xe2x80x9d that prevent the top assembly from being pushed so far into the battery container that it contacts the top of the cathode. It is preferred that the top assembly is not pushed against the cathode, because when this happens, the cathode can buckle. When the cathode is buckled or deformed, electrolyte can sometimes leak out of the battery.
In another aspect, the invention features a metal-air battery having a positive end and a negative end that includes: (a) a container having a plurality of louvers including leaves, wherein at least three of the louvers have ends located toward an end of the battery; (b) an anode; (c) a cathode; (d) a separator between the anode and the cathode; and (e) a top assembly in contact with a plurality of supports in the wall of the container.
In this battery, the louvers promote air circulation across the cathode surface; the supports minimize the damage to the cathode. Without the supports, the top assembly can be seated improperly, which in turn can result in damage to the cathode and/or electrolyte leakage from the battery during storage and use.
As used herein, xe2x80x9ctowardxe2x80x9d means at a position on a member, relative to a given point on that member, within 20% more preferably 10% or 5%, of the total length of the member. A feature located xe2x80x9ctowardxe2x80x9d an end of a container having a length of 10 cm is within 2 cm of that end of the container, and is preferably within 1 cm or 0.5 cm from the end.
As used herein, a xe2x80x9ctop assemblyxe2x80x9d means any member for a metal-air battery that includes a cavity that can accommodate a cathode, an end cap that can form an end surface of a battery container, a current collector, and means for engaging a support on the wall of the battery container.
Other features and advantages of the invention will be apparent from the description of the preferred embodiment thereof, and from the claims.